Effects of supplemental nitrogen application on physiological characteristics, dry matter and nitrogen accumulation of winter rapeseed (Brassica napus L.) under waterlogging stress

Waterlogging stress is a common limiting factor for winter rapeseed, which greatly affects the growth and potential production. The present study was conducted to investigate the effects of waterlogging with different durations (0day (D0), 6days (D6) and 9days (D9)) and supplemental nitrogen fertilization (N1, 0 kg ha−1; N2, 30 kg ha−1; N3, 60 kg ha−1 and N4, 90 kg ha−1) on the physiological characteristics, dry matter and nitrogen accumulation in winter rapeseed (Chuanyou36). The results showed that the supplementary application of nitrogen fertilizer could effectively improve the physiological indexes of winter rapeseed in both pot and field experiments. The supplemental nitrogen increased the chlorophyll content in leaves, enhanced the activities of SOD, CAT, and POD, and decreased the MDA content in leaves and roots of rapeseed. The chlorophyll contents, the antioxidant enzyme activity of leaves and roots significantly increased under D6N3 and D9N4 conditions in both (pot and field) experiments. However, MDA contents significantly decreased compared with waterlogging without nitrogen application. Moreover, the application of nitrogen fertilizer after waterlogging increased the accumulation of dry matter and nitrogen in rapeseed at different growth stages. Therefore, waterlogging stress significantly inhibited the growth and development of rapeseed, but the application of nitrogen fertilizer could effectively reduce the damage of waterlogging. The N-induced increase in waterlogging tolerance of rapeseed might be attributed to the strong antioxidant defense system, maintenance of photosynthetic pigments and the nutrient balance.